Japanese blog Macotakara is reporting that Hitachi Displays and Sony Mobile Display Corporation have already begun shipping four-inch displays for a "new iOS device", as well as a new iPad-sized LCD display.
According to the blog's source: "Hitachi Displays, Ltd. and Sony Mobile Display Corporation started to ship four-inch LCD for new iOS device and LCD for iPad 3."
Although the source doesn't mention a specific iOS device for the new four-inch screen, Apple's next iPhone iteration is a major contender. After all, one of iLounge's "most reliable" sources claimed just last week that the iPhone 5 will sport a larger screen.
Apple's previous iPhone models have all sported 3.5-inch displays, but these are starting to look small when compared with some other phones on the market.